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Surface Tension and Inverse Square Law
Name: Justin
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Since Van der Waals and surface tension are really aspects of
electrical forces. Does that mean that surface tension and Van der Waals
follow inverse square laws?
Replies:
Hi Justin,
I am a little confused by what is meant by 'aspects of electrical
forces'. It is true that electrons play a huge role in determining an
atom's properties, including its chemical and physical properties --
including surface energy (surface tension) and van der waals forces.
However, the basis for each of these properties is very different,
and, perhaps not surprisingly, so are the physics around them.
It is a good idea to be a little more specific when defining
mathematical relationships like 'inverse square law'. Between what two
quantities do you mean? For van der Waals forces, I am guessing you
mean the force between two molecules with respect to distance (it
turns out it is not a square relationship -- it is highly repulsive when
close, weakly attractive at middle distances, and nearly zero at long
distances). For surface tension, I am not sure which relationship you
mean.
The bottom line is that even if two properties share a broad,
qualitative similarity, it is still very possible (even likely) that
they are very different.
Hope this helps,
Burr Zimmerman
Not necessarily so. Not all electrical fields (forces) obey an inverse
square law. Two "point" charges do, but other interactions of electrons
(which form the 'outside' of atoms and molecules) may interact quite
differently since effects other than the inverse square law apply. For
example: Van der Waals forces are more commonly expressed by the "6-12"
potential energy V(r), that is: V(r) = A x [ -B/r^6 + C/r^12]
The "attraction" (-1/r^6) is fairly long ranged) and the "repulsion"
(+1/^12) increases rapidly as the distance "r" decreases.
Vince Calder
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Update: June 2012
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